The moment came on the first Friday on the last month of the year, on the courts of the Elite Squad Tennis Club in Overland Park, Ks., just outside of Kansas City. It happened at the end of a long week of two-a-days, hours into an already-grueling session, at what would be the toughest moment of his training week. Jack Sock had just finished more than a dozen sets of a court-coverage drill—as Sock hit balls to his coaches, Mike Wolf and Troy Hahn, on the opposite side the court, they quickly returned them to the other end, but just away from Sock, out of his reach, forcing him to constantly race back and forth. Completely gassed, Sock turned to his coaches.

“Let's keep going,” he said.

With the same rules in place—hit the ball back in play on one bounce and sustain the intensity level—Sock resumed the drill.

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“He took himself to a place few people are willing to go, the next level of putting yourself through pain and concentration that is required if you want to compete against the Top 10 guys,” says Wolf, who has worked with Sock since he and his older brother, Eric, started to make weekend trips from their home in Lincoln, Neb., to Kansas City to train at Wolf’s academy. “I told him: ‘This was one of the best training moments I’ve ever had with you. I haven’t seen that out of you in a number of years. That is where people compete to win Grand Slams, on the practice court.’”

After finishing the year with a long fall season—33 matches in 33 days, between singles and doubles—perhaps Sock’s elevated level has something to do with being back in a familiar place. The 24-year-old American ended the season ranked No. 23, and after Paris, he took a week off to go see friends and enjoy a weekend in Athens, Ga., to watch some Bulldogs football. After spending Thanksgiving in Lincoln with his family, it was back to work.

“In the offseason, you can definitely get after it a little more,” Sock said in a post-workout interview in Orlando, Fla., in November. “You can have very intense workouts and not have to worry about a match coming up in a day or two or in the next week... . [There’s] time now to set a really good foundation for the long season we have."

For the 2017 season, Sock will continue to work with Hahn full-time but he has also signed Wolf on in a more extensive role, as he will travel with Sock for six to 10 tournaments during the year. Wolf says the move was part of a natural progression, as Sock established a full-time residence in Kansas City and returned often for training with his longtime coach and mentor. For Sock, being back in the place where he began his tennis career is extra motivating.

“It starts with family—they’ve sacrificed so much for me, with my parents moving away from each other when we were young, for tennis,” Sock says. His father stayed in Lincoln to work while his mother took him to Kansas City to train on weekends. “When I was the young guy on tour, I don’t think I really grasped what it actually takes to be at this level. The more time you spend on tour, around the top guys especially, you see what they do, the work, the preparation, the organization they have going into their training. It all leads up to playing great tennis. It really opens your eyes.”

For this offseason, Sock has incorporated boxing into his regimen and he also makes sure to work on his hip, shoulder and forearm muscles to keep up strength and mobility. Wolf says he has also done a good job of getting “back to the basics” when it comes to his training.

“I think that one of the best parts of being back in Kansas City is that we’ve gotten back to simple,” says Wolf. “Not complicated. Energy is very focused. What we come out to do every day in practice is very intentional. And so there is very little time wasted.”

Sock will start his season at the Australian Open in January as he looks to ascend the ATP rankings. To become the top-ranked American, he’ll have to unseat his good friend and current World No. 19, John Isner, someone he says has helped push him to find that next level.

“Honestly. I’ve learned a lot from him. He’s been around for a long time now. Having an American like that, who’s currently playing, that you can draw information from, it really helps with the ins and outs of the ATP Tour, how to be a professional,” Sock says. “It definitely makes the year—when you’re gone like that on the road all the time—a little bit easier when you have a close friend with you.”

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After winning his first career title in Houston in 2015, Sock came up short this year, losing in the finals in Auckland, Houston and Stockholm. As he gets ready for Australia, Sock hopes his structured, intense offseason training will serve as a foundation for better results in 2017.

“I think I made great progress this year on and off the court. I think I matured in a lot of ways,” he says. “Next year I definitely want to compete to win some more titles. I got close a few times and had some good runs in tournaments, but definitely playing the second week of Slams is a place I think I can be.”